Just a warning: Do not attempt to change the /usr/bin/python symlink to point to python3 instead of 2.7. Many programs available in the Ubuntu repos require /usr/bin/python to be compatible to python 2.x.
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soulsourceJul 17 '13 at 8:17

@soulsource, yeah I'm aware of that. that's why i asked is there an "upgrade" option available or not.
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GiriJul 17 '13 at 8:24

I think the answer by Radu Rădeanu is already quite close to the optimal solution. It only applies to one user, and is only in effect for directly running python typing the python command, not affecting programs with a #!/usr/bin/python shebang.
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soulsourceJul 17 '13 at 8:44

1

Ah, now I got what you meant with upgrade... Actually the Ubuntu developers are working on that: wiki.ubuntu.com/Python/3 "It is a release goal for Ubuntu 14.04 LTS to have only Python 3 on the desktop CD images."
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soulsourceJul 17 '13 at 8:45

For both Ubuntu and Debian, we have ongoing project goals to make Python 3 the default, preferred Python version in the distros.

What this does not mean:

/usr/bin/python will point to Python 3. No, this is not going to happen (unless PEP 394 advocates otherwise, which is doubtful for the foreseeable future). /usr/bin/python and /usr/bin/python2 will point to Python 2.7 and /usr/bin/python3 will point to the latest supported Python 3 version.

Python 2 will be removed from the archive. No, this is not going to happen. We expect Python 2.7 to remain supported and available in Ubuntu for quite a long time, given that PEP 373 promises upstream bug fix maintenance support until 2020.

It is not recommended to change the symbolic link because of other package dependencies, but they "have ongoing project goals to make Python 3 the default, preferred Python version in the distros".

For CLI use, like @Radu Rădeanu, I would recommend putting an alias in the user's ~/.bashrc, .bash_aliases file (the different files, including ~/.bash_profile, are all loaded together and are simply for organizational purposes).

Such as:

alias python=python3

or

alias python='/usr/bin/python3'

Scripts can then start with something like:

#!/usr/bin/env python

instead of

#!/usr/bin/python3

I would still recommend using #!/usr/bin/python3 in scripts for simpler cross-compatibility.

Beginning users may not be able to easily adapt the linked answer to a different situation. In addition to crediting the earlier answer, it would be good to lay out the steps needed for Python.
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chaskesOct 18 '13 at 14:47